Metal sulfates have been widely used in polyester. U.S. Pat. No. 4,043,971 disclosed a polybutylene terephthalate molding compositions of improved tracking resistance, which contained calcium sulfate or barium sulfate 10 to 40% by weight. Calcium sulfate or barium sulfate powder was added to the polyester after polymerization. Calcium sulfate and barium sulfate are not soluble in alcohol and water. It is difficult to form stable slurry for use in polyester polymerization.
U.S. Pat. No. 6,699,546 disclosed a hot-fill polyester bottle containing barium sulfate 40-50 ppm for improved crystallization and strength. China Patent 03113436.X disclosed a polyester sewing thread, which contained barium sulfate 0.10% to 0.15% for improved fiber strength and spinning performance. In these inventions, barium sulfate powder was dispersed in glycol through milling, the slurry was then added to polyester polymerization process. Barium sulfate was poorly dispersed in glycol. After agitation stops for a few hours, the slurry separates into two layers, clear liquid on top, and barium sulfate precipitates on the bottom.
China patent 01107744.1 and 01115055.6 disclosed a collosol of barium sulfate in glycol. This collosol contained barium sulfate 1-30% (preferably 2-25%), C2-C4 glycol 68-97% (preferably 73-96%), and balancing water less than 2% by weight. The preparation was complicated. First, barium hydroxide octahydrate was dissolved in glycol and water at hot temperature and then filtered. Dilute sulfuric acid of 0.5-2.0 mol/L (4.7-17.2% by weight), preferably 1.5 mol/L (13.2% by weight), was added to react with barium hydroxide. The colloidal must be distilled at 180-197° C. to remove water. Barium sulfate particle size was 10 to 100 nm. Barium sulfate particles of this size are very easy to form large agglomerates, which cause non-uniform dispersion in polyester. The distillation to remove large volume of waste water requires large amount of energy input, which is an environmental concern.
Therefore, there is a need to develop a metal sulfate alcohol composition for use in polyester polymerization, which is stable without agitation, relatively easy to manufacture, and does not produce large volume of waste water; appropriate particle sizes are less likely to form agglomerates, therefore uniform dispersion in polyester.